Intravascular stents are known in the art. These stents can be tubular in form. Numerous tubular stent designs are now on the market. Many of them comprise a radially expandable mesh type metal network, either in the form of a fine wire mesh or of a tube wall wherein a recurring pattern of holes have been cut (e.g. by means of a laser) in order to form a so-called slotted tube stent. Stents can also have an expandable tubular spring like structure such as a so-called coil stent or a so-called ring stent.
A stent may be introduced into an artery according to following method. Protected by a sheath the stent is advanced across the lesion in the artery. Once in position the sheath is removed from the stent. By means of a balloon catheter the stent is radially fully expanded. Thereafter the catheter is withdrawn. So a stent must be flexible enough to pass through the vasculature without causing damage. The stent must be strong enough to support a diseased vessel and the stent must survive crimping onto a catheter followed by radial expansion without breaking or weakening. These severe requirements often lead to the choice of metal as material for the stents. The metal is preferably stainless steel, titanium, tantalum, platinum, nitinol or a nickel-titanium alloy.
However, metals in general, and stainless steel in particular, tend to be thrombogenic, i.e. metals encourage the formation of blood clots. Metal stents also cause neointimal hyperplasia. This is one of the reasons why the surfaces of prior art stents have been provided with a biocompatible layer.
WO-A-99/62572 of applicant discloses an intravascular metal stent a major part of the surface of which has been coated with a biocompatible layer containing a diamond like nanocomposite material.
Although showing a substantial reduction in thrombogenecity and neointimal hyperplasia, metal may still be present on the surface after the above-mentioned crimping followed by an expansion of the stent. This may lead to adverse tissue reactions.